The present invention relates to an outer needle of an anesthetic needle assembly to be injected into an epidural area of the body.
The anesthetic needle assembly is composed of outer and inner needles, of which the inner needle is taken out of the outer needle after the needle assembly is injected into the epidural area of a patient. Then, the outer needle is used as a guide for insertion of a catheter or anesthetic needle.
The outer needle is known as a spinal needle that is made of a stainless steel tube, of which the bevel cut end is bent to form a distal end of the outer needle. The distal end has an annular cutting edge forming an elliptic, planar opening. The annular cutting edge has a relatively sharp cutting angle, for example, 30 degrees at an outer frontal corner part thereof.
As seen in FIG. 5, the known outer needle 8 has a distal end with a somewhat sharp curve. When the catheter or anesthetic needle 10 is inserted into the outer needle 8, it has the forward end thereof butting the inner surface of the distal end 9 of the outer needle 8 in the steeply inclined direction with the result that it cannot pass through the distal end 9 without meeting with a large frictional resistance. This leads to a disadvantage that it is not easy for the catheter or anesthetic needle to have the forward end to project out of the annular cutting edge 18 of the outer needle 8.
As seen in FIGS. 6 and 7, the other outer needle 19 has been proposed to have a distal end 21 with a relatively gentle curve, in order to solve the aforementioned disadvantage. The outer needle 19 allows the catheter or anesthetic needle 20 to easily project the forward end from the annular cutting edge 22, because there is a fair chance for the forward end to pass through the distal end without butting the inner surface of the distal end 21. Although the catheter or anesthetic needle 20 is inserted in the outer needle 19 in a manner that the forward end thereof knocks the inner surface of the distal end 21, it buts the inner surface of the distal end 19 in the gently inclined direction with the result that the forward end can pass through the distal end 19 and project from the annular cutting edge 22 without meeting with a large frictional resistance. However, the outer needle 19 has the problem that the annular edge 22 is apt to wound the epidural membrane when injected into the epidural area. The other problem is that the catheter is sometimes caught and damaged by the annular edge 22 when it is drawn out from the outer needle 19.
Thus, the annular cutting edge 22 has a sharp cutting angle at the outer frontal corner part 23 thereof defined by the major axis and the mother line of the outer needle 19 with the result that the outer needle 19 is apt to wound the epidural membrane. When the distal end 21 with a relatively gentle curve is injected in the epidural area, the outer frontal corner part 23 with a sharp cutting angle touches the epidural membrane in the near vertical direction. The annular cutting edge 22 also has a sharp cutting angle at the inner frontal corner part 24 thereof defined by the major axis and the mother line of the outer needle 19 with the result that the outer needle 19 sometimes damages the catheter. When the catheter is drawn from the outer needle, it approaches the rear narrow wedge-shaped portion of the elliptic planar opening surrounded by the annular cutting edge 22 whereby the catheter contacts the inner frontal corner part 24 with a sharp cutting angle.
The present invention as claimed is intended to solve the problems described above and provide an outer needle of an anesthetic needle assembly for epidural use. The needle is improved as follow:
1. It has an annular cutting edge in which the outer frontal corner part is prevented from injuring the epidural membrane when injected into the epidural area.
2. It has an annular cutting edge in which the inner frontal corner part is prevented from catching or damaging the catheter being drawn out of the outer needle through the rear portion of the annular cutting edge.
3. It allows an anesthetic needle to project from the forward end portion thereof, i.e., from the annular cutting edge, with ease.
The anesthetic needle assembly to be injected into the epidural area of a patient has an outer needle that is mostly made of a stainless steel tube. According to the present invention, the outer needle has a distal end portion bent in a manner that, when an anesthetic needle has the forward end thereof contacted with the inner surface of the distal end portion of the outer needle, the front end slides out of the annular cutting edge of the outer needle through the inner surface of the distal end. The annular cutting edge has an opening with major and minor axes and is composed of bifurcated forward convex surfaces and bifurcated rear concave surfaces with respect to a plane including the major and minor axes. The outer needle has dull cutting angles at the outer and inner frontal corner parts of the waved annular cutting edge in comparison with the known outer needle having sharp cutting angles at the outer and inner frontal corner parts of the planar annular cutting edge.
In preference, the annular cutting edge has such bifurcate convex and concave surfaces that are symmetrical with respect to a plane including the major axis and perpendicular to the minor axis to form a smooth continuous wave surface. But, it is also possible that each of the convex and concave surfaces is composed of discontinuous planar or curved surface portions and the convex and concave surfaces are crossly or stepwise joined to one another.
In preference, the respective cutting angles at the outer and inner frontal corner parts of the annular cutting edge are in a range of 60 to 90 degrees that are twice or more as large as those of the known planar annular cutting edge.
In preference, the annular cutting edge has a top view of an extended circle or oblong with four round corners and two outwardly curved long sides, in order to prevent the catheter from being wedged in the rear portion of the annular cutting edge when the catheter is drawn out. The catheter contacts the inner frontal corner part of the annular cutting edge without receiving any damage because the corner part has a dull cutting angle.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.